Ming seem to be doing this upgrade themselves but it only looks like its come out in places like Korea, so far. The Ming version of the upgrade comes with a smaller front ‘chainwheel’ and a shorter belt, to give a lower ‘low’ gear and a more reasonable ‘high’ gear.
(there again, add 18inch wheels and the ratios can be raised higher)
you are not the only person who wants this …
lets’ hope Ming supply a lowcost upgrade kit (ie ATS version of Schlumpf, belt and chainwheel).
Personally, I like the simplicity of single speed - ( and it seems, from all the track bikes I see, that fashion is catching up with me, rather than the other way round as is normal 
).